LTM4616_15 Datasheet, PDF (16/30 Pages) Linear Technology – Dual 8A per Channel Low VIN DC/DC Module Regulator

LTM4616
Applications Information
coincident tracking. The LTM4616 uses an accurate 10k
resistor internally for the top feedback resistor. Figure 5
shows an example of coincident tracking:
Slave
=
⎛
⎝⎜¹⁺
10k ^⎞
R_TA ⎠⎟
•
V_TRACK
V_TRACK is the track ramp applied to the slave’s track pin.
V_TRACK has a control range of 0V to 0.596V, or the internal
reference voltage. When the master’s output is divided
down with the same resistor values used to set the slave’s
output, then the slave will coincident track with the master
until it reaches its final value. The master will continue to its
final value from the slave’s regulation point. Voltage track-
ing is disabled when V_TRACK is more than 0.596V. R_TA in
Figure 5 will be equal to R_FB for coincident tracking.
The track pin of the master can be controlled by an external
ramp or by R_SR and C_SR in Figure 5 referenced to V_IN.
The RC ramp time can be programmed using equation:
t
=
⎛⎛
– _⎝⎜ln_⎝⎜1–
0.596V^⎞
V_IN ⎠⎟
•
R_SR
•
⎞
C_{SR⎠⎟}
Ratiometric tracking can be achieved by a few simple
calculations and the slew rate value applied to the mas-
ter’s track pin. As mentioned above, the TRACK pin has
a control range from 0V to 0.596V. The master’s TRACK
pin slew rate is directly equal to the master’s output slew
rate in Volts/Time:
MR
SR
•
10k
=
R_TB
where MR is the master’s output slew rate and SR is the
slave’s output slew rate in Volts/Time. When coincident
tracking is desired, then MR and SR are equal, thus R_TB
is equal to 10k. R_TA is derived from equation:
R_TA
=
V_FB
0.596V
+ ^VFB – ^VTRACK
10k R_FB R_TB
where V_FB is the feedback voltage reference of the regula-
tor and V_TRACK is 0.596V. Since R_TB is equal to the 10k
top feedback resistor of the slave regulator in coincident
tracking, then R_TA is equal to R_FB2 with V_FB = V_TRACK.
CLKIN1
V_IN 4V TO 5.5V
RUN
10µF
R_SR
C_SR
MASTER
3.3V
R_TB
10k
R_TA
6.65k
RUN
10µF
SW1
V_IN1
SV_IN1
RUN1
PLLLPF1
MODE1
PHMODE1
TRACK1
V_IN2
SV_IN2
RUN2
PLLLPF2
MODE2
PHMODE2
TRACK2
SW2
CLKIN1
SGND1
CLKOUT1 CLKIN2
LTM4616
GND1 SGND2
CLKOUT2
V_OUT1
FB1
I_TH1
I_THM1
PGOOD1
BSEL1
MGN1
V_OUT2
FB2
I_TH2
I_THM2
PGOOD2
BSEL2
MGN2
GND2
4616 F05
R_FB1
2.21k
R_FB2
6.65k
PGOOD
BSEL
100µF
V_IN
50k
MASTER
3.3V/7A
50k
SLAVE
1.5V/8A
100µF
100µF
16
FOR TRACK1:
1. TIE TO VIN TO DISABLE TRACK WITH DEFAULT 100µs SOFT START
2. APPLY A CONTROL RAMP WITH R_SR AND C_SR TIED TO V_IN WITH t = –(ln(1–0.596/V_IN) • R_SR • C_SR))
3. APPLY AN EXTERNAL TRACKING RAMP DIRECTLY
Figure 5. Dual Outputs (3.3V and 1.5V) with Tracking
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